1. Field of the Invention
This invention relates to an antimicrobial agent for animals comprising as an effective component a racemate or a 3S-type compound of a pyrido[1,2,3-de][1,4]benzoxazine derivative represented by the formula (I): ##STR2## wherein R is a C.sub.1-6 alkyl group (provided that R cannot be a methyl group when the pyrido[1,2,3-de][1,4]benzoxazine derivative is a racemate), or a salt or a hydrate thereof. The antimicrobial agent of this invention is useful for the prevention, cure, or treatment of various infectious diseases of animals.
2. Description of the Background
The increased number of livestock and poultry confined to a unit area by the current stockbreeding practices gives rise to the proliferation of various infectious diseases among farm animals and domestic fowl. Damage caused by such infectious diseases has been increasing yearly, posing an economic problem to the industry.
Conventionally, antibiotics such as tylosin, oxytetracycline, etc., and synthetic antimicrobial agents such as oxolinic acid, piromidic acid, etc. have been added to feed or water, orally administered, or injected to animals for the prevention and cure of their infectious diseases.
These conventional antimicrobial agents, however, have drawbacks such as insufficient antimicrobial activity, a narrow antimicrobial spectrum, development of microbial resistance to the agents, low disease-curing effect, inadequate safety, side effects, high production costs, and the like.
Among pyrido[1,2,3-de][1,4]benzoxazine derivatives of the above formula (I) a compound which is a racemate has been reported in Japanese Patent Laid-open No. 184014/1985. Japanese Patent Laid-open No. 116217/1984 discloses antimycoplasmal activity of ofloxacin. These compounds, however, possesses only a narrow antimicrobial spectrum, and their antimicrobial activity is not necessarily sufficient.